Traditional color imagers or image sensors or pixelated imaging arrays use a Bayer pattern of pixels and pixel filters, which has a red-green-green-blue (R-G-G-B) pixel/filter configuration (such as shown in FIG. 1). In such a pixelated array, the sensor includes individual optical filters that transmit red, green or blue colors and that are disposed at or coated on the individual pixels. Thus, there is a “red pixel” 12a, a “blue pixel” 12b and two “green pixels” 12c arranged to form a 2×2 sub-array 10 that is repeated over the pixelated array.
The three color filters (R, G, and B) not only pass ranges of wavelengths or spectral bands that are corresponding to red, green and blue colors, they also pass through a significant amount of wavelengths in the infrared (IR) or near infrared (NIR) region or band of the spectrum. Therefore, the color imager sensitivity or quantum efficiency spectrum typically has a rich IR or NIR response even with the R, G, and B color pixels. For example, a typical silicon CMOS color sensor's spectrum response is shown in FIG. 2. The IR response of the R, G and B pixels is comparable or higher than the pixels' response of visible spectrum. The IR light from the environment thus may wash-out the color response in the visible spectrum and thus may distort the image color reproduction. This is often referred to as IR contamination. In a traditional color camera, in order to reproduce a true color image, an IR cut-off filter is usually used to cut off or reduce light or energy at or in the IR band or region of the spectrum so as to allow only (or substantially only) the visible light to pass through the filter so as to be imaged by the RGGB pixels, in order to reduce or limit or substantially eliminate the IR contamination. Such an IR cut-off filter is typically made of multilayer coatings on a glass or plastic element, such as a flat glass plate, that is added on to a lens assembly of the imager or onto a surface of a lens element of the lens assembly of the imager. The coating process and added material increase the cost of the lens, sometimes significantly.
On the other hand, for IR imaging applications that have the main spectrum of interest in the NIR region of the spectrum, where silicon CCD or CMOS can provide good quantum efficiency, one may need to cut the visible spectrum off from the light reaching the imager. A long pass filter that is a multilayer coating on a glass or plastic flat plate is typically used to let through NIR light only. Security cameras and some special industrial machine vision systems are among the applications of such a filter-imager configuration. For cameras that operate in both day and night for such applications, mechanical switches of IR cutoff filters and IR pass filters are used on silicon CMOS or CCD cameras. The additional cost of two filters and mechanical switches, as well as the reliability of the moving mechanical switch, make such systems undesirable, and such a design is not suitable for automotive or consumer digital cameras or cell phone cameras.